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  1. #1
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    Merc 250EFI possible fuel pump problem need help

    Engine is a 2003 Mercury 250 EFI story yesterday I went to take boat out after installing two new group 31 agm batteries when I previously had lead acid batteries. Unfortunately I don't think it's related to them.I noticed that when taking off the first time the boat had no power wouldn't plane out I almost thought there wasn't getting any electrical that's how sluggish it felt I noticed when trying to take off it felt as if the boat had no power, couldn't plane, max rpm of 2000.

    I noticed fuel bulb was soft so after looking at the motor a little more I noticed that one of the hoses on the low pressure diaphragm pump might not have seated great so after tightening it the bulb have been staying tight. I had rebuilt it last week. I did take the boat out after doing it and it ran great last time however maybe the hose worked itself loose while trailering. My theory is maybe the high pressure pump burned out from me trying to give the boat gas that it couldn't supply.

    Voltage checked out good to high pressure fuel pump harness 12v upon turning key, however fuel pressure is low. First time I checked it got to 33psi but then after than no more than 30. Spec is supposed to be 40-45 psi. Even when running it stayed at 30. I'm wondering if you think its a fuel pressure regulator or the high pressure fuel pump itself?
    Last edited by LIGlastron; 05-31-2020 at 06:49 PM.

  2. #2
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    If you can amp draw the pump.

    if amp draw is good check the regulator and filters screens.

    good amp draw can still be bad pump just mechanical parts not motor.

  3. #3
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    Quote Originally Posted by Motv18 View Post
    If you can amp draw the pump.

    if amp draw is good check the regulator and filters screens.

    good amp draw can still be bad pump just mechanical parts not motor.
    I should have mentioned about 3 months ago I had taken vst apart and cleaned the inlet screen on hpfp and installed new gas/water seperator. The screen was definitely clogged a bit then.

    Today I noticed in my Merc manual that there is a final filter it's called which is after the hpfp or on the outlet right by the Schrader valve. It is a cone shaped filter. This filter definitely had some accumulation. Not major but the filter was very fine and I could see it affecting flow. But this issue overall seems a loss of fuel under load.

    I did notice something interesting. When I trimmed motor up where prop was slightly out of water if I revved that way I could get motor above 2k, however in driving 1900-2k was max rpm. At first I thought it was the guardian system however this seems to change that theory.

    With what I was saying earlier with the diaphragm pump maybe having a loose connection to the point where the fuel bulb wouldn't stay firm do you think this could have caused a bit of a high preasure fuel pump starvation now causing pump failure? Any way to test fuel pressure regulator?
    Last edited by LIGlastron; 05-31-2020 at 09:52 PM.

  4. #4
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    If you pinch the line on the FPR while the motor is running the fuel pressure should spike.


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  5. #5
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    Quote Originally Posted by InjectorService View Post
    If you pinch the line on the FPR while the motor is running the fuel pressure should spike.
    If it does spike does it mean fpr is bad?

  6. #6
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    im in Plainview and am having similar problems ran good then started to struggle out of the hole on Saturday in my activator. I pulled the injectors and vst. to have them flowed and rebuilt

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